Liquid crystal devices, organic EL devices and the like have been developed as energy-saving devices that have supersedes CRTs. The next goal herein is achieving a flexible display overall, in applications such as electronic paper and the like, to which end there are required pliable, heat-resistant films. However, although conventional materials, for instance plastic films, are pliable, their heat resistance and gas barrier properties are arguably insufficient, while thin-sheet glass, which has excellent light transmittance and heat resistance, is problematic in being insufficiently pliable. Moreover, thin-sheet glass can be manufactured only down to a thickness of about 0.4 mm, which adds to the pliability problem the difficulty of achieving lighter weights. There is an urge thus for the development of a film-like material that combines pliability, heat resistance, transparency and gas barrier properties. In terms of realizing pliability and light weight, the film should be as thin as possible, while the film substrate should have surface smoothness, resistance to chemicals, as well as dimensional stability or low dilatability.
An inorganic layered compound such as swelling clay or the like is known to form a film having evenly oriented particles by dispersing the inorganic layered compound in water or alcohol, spreading the dispersion onto a glass sheet, and letting it stand to dry. For example, oriented specimens for X-ray diffraction have been prepared using this method (See Non-patent Document 1). However, when a film was formed on a glass sheet, it was difficult to strip the inorganic layered compound thin film off the glass sheet, while cracks formed in the thin film during strip-off, among other problems that made it difficult to obtain a self-supporting film. Even if the film was stripped successfully off the glass sheet, the resulting film was brittle and lacked sufficient strength. To date, it has been difficult to manufacture an even-thickness film free of pinholes and having excellent gas barrier properties.
Meanwhile, various polymeric resins are used as molding materials, and also as dispersants, thickeners, binders, and as gas barrier materials having inorganic materials blended therein. For instance, a known film having gas barrier properties may be obtained by manufacturing a film having a thickness of 0.1 to 50 μm from a composition comprising 100 parts by weight of a mixture of (A) a highly hydrogen-bondable resin containing two or more carboxyl groups per molecule, such as polyacrylic acid or the like, and (B) a highly hydrogen-bondable resin containing two or more hydroxyl groups in its molecular chain, for instance starch or the like, to a weight ratio A/B=80/20 to 60/40, and 1 to 10 parts by weight of an inorganic layered compound such as a clay mineral or the like; and by subjecting then the film to a thermal treatment and an electron beam treatment (See Patent Document 1). The above film is problematic, however, in that the main component thereof is a water-soluble polymer resin, so heat resistance is not very high.
Also, a laminated film having excellent moisture resistance and gas barrier properties, suitable for food packaging, can be obtained by laminating a layer composed of a resin composition comprising a resin and an inorganic layered compound between two polyolefin-based resin layers (See Patent Document 2). In this case, however, the layer of resin composition comprising an inorganic layered compound is merely used as part of a multilayer film, and not on its own as a self-supporting film. Also, the heat resistance of such laminated films is governed by the organic material having the lowest heat resistance in the composition, in this case a polyolefin, which is a material that does not afford high heat resistance.
Recently, there have been manufactured inorganic layered compound thin films using the Langmuir-Blodgett method (See Non-patent Document 2). This method, however, involves forming an inorganic layered compound thin film on a substrate surface finished with a material such as glass or the like, and precludes achieving an inorganic layered compound thin film strong enough for a self-supporting film. Various other methods have also been reported for preparing functional inorganic layered compound thin films and the like. For instance, there is disclosed a method for manufacturing a clay thin film in which an aqueous dispersion of a hydrotalcite-based interlayer compound is made into a thin film and dried (See Patent Document 3); a method for manufacturing a clay mineral thin film in which the bond structure of a clay mineral is oriented and fixed through a thermal treatment that promotes a reaction between the clay mineral and phosphoric acid or phosphoric acid groups (See Patent Document 4); and an aqueous composition for a coating treatment, containing a complex compound of a divalent or higher metal and a smectite-based clay mineral (See Patent Document 5), to cite just a few of the many such examples. However, none of the above methods affords an inorganic layered compound oriented self-supporting film having enough mechanical strength to be used as a self-supporting film, and being imparted with gas barrier properties due to highly oriented clay particle layers.
In the cosmetic and pharmaceuticals fields, meanwhile, there have been proposed composites of inorganic layered compounds and organic compounds, for instance advantageous organic composite clay minerals (for instance, see Patent Documents 6 and 7), or in the manufacture of a drug for treating wet athlete's foot, comprising a mixture of a clay mineral, an acid, and an enzyme (for instance, see Patent Documents 8 and 9). Nevertheless, the fact remains that these organic composite clay minerals have failed thus far to be used as self-supporting films. There is thus an urgent need in this technical field for the development and practical application of a novel inorganic layered compound film having enough mechanical strength to be used as a self-supporting film.
Patent Document 1: Japanese Patent Application Laid-Open No. H10-231434
Patent Document 2: Japanese Patent Application Laid-Open No. H07-251489
Patent Document 3: Japanese Patent Application Laid-Open No. H06-95290
Patent Document 4: Japanese Patent Application Laid-Open No. H05-254824
Patent Document 5: Japanese Patent Application Laid-Open No. 2002-30255
Patent Document 6: Japanese Patent Application Laid-Open No. S63-64913
Patent Document 7: Japanese Patent Application Publication No. H07-17371
Patent Document 8: Japanese Patent Application Laid-Open No. S52-15807
Patent Document 9: Japanese Patent Application Laid-Open No. S61-3767
Non-patent Document 1: Haruo Shiramizu, “Clay Mineralogy (Nendo Kobutsu Gaku)—Basics of Clay Science”, Asakura Shoten, p. 57 (1988)
Non-patent Document 2: Yasufumi Umemura, Nendo Kagaku (Clay Science), Vol. 42, No. 4, 218-222 (2003)